This invention relates to a magnetic card which is able to keep permanent signals for preventing its fraudulent misuse within the card.
The increasing use of magnetic cards including keys, identification passes, passports, credit cards or tokens etc., has led to the introduction of sophisticated techniques to prevent their fraudulent misuse.
In particular British Patent specification No. 1,331,604 describes a security card formed of a layer of anisotropic magnetic particles which in spaced regions of the layer are fixedly aligned along a predetermined direction, and in the remaining regions are not so aligned or are aligned along a substantially different direction. By uniaxially magnetising the aligned particles, the pattern of remnant magnetisation becomes permanent, and can only be destroyed if the document is destroyed also.
Such a pattern, therefore, which is sometimes referred to as a magnetic "watermark", or as forming a "permanent magnetic structure", may be used as a permanent identification or verification code, since the regions of differently aligned particles may be assigned different significance, e.g. a binary "1" or "0".
The card of this structure may be passed over a suitable reading device, for example a vertical or horizontal magneto resistive (MR) head.
Since, however, the mechanism for applying the special magnetic material on the card which can record for memory the permanent information was used in manufacturing the above structured card and its mechanism was too expensive, one problem of this technique was that the cost of the card was too high, and its processes were complicated.